This invention relates to communications systems, and particularly to one using a balloon tether as a long antenna for very low frequency transmission. It relates specifically to the attachment mechanism used for connecting the VLF transmitter to a vertically suspended antenna/tether cable.
Communications systems operating at high frequencies utilize a physically large tower as a monopole antenna or to support a monopole antenna. At very low frequencies, a tower is physically and economically impractical. The reason for this is that ideally, the antenna should be a quarter wavelength in height. However, a very low frequency (VLF) system operating at 61 kHz would need an antenna over 4,000 feet high.
Exemplary in the art of VLF communications systems is the disclosure of U.S. Pat. No. 4,476,576 issued to Myron S. Wheeler et al, the disclosure of which is incorporated by reference. Wheeler et al disclose a VLF communication system that uses an aerostat to support a cable that serves as both a tether and an antenna.
The electromechanical cable used in the VLF communication of Wheeler et al is directly connected to a winch, which deploys it, and is electrically connected to a VLF transmitter. The VLF transmitter can operate at voltages of about 62 kv. During operation, there exists a requirement to protect the tether base from the effects of high voltage. More specifically, corona discharges from the high voltage can cause a failure of the antenna by destructive ionization at the point where the feed cable from the transmitter connects with the antenna.
From the foregoing discussion, it is apparent that there currently exists the need to protect the antennas of VLF communication systems from corona discharges. The present invention is intended to satisfy that need.